1. Field of the Invention
The present invention relates to receiving devices, receiving methods, and programs, and particularly to a receiving device, a receiving method, and a program that are so configured as to allow suppression of the power consumption in the case of receiving warning information in the waiting state.
2. Description of the Related Art
As a modulation system for digital terrestrial broadcasting, there has been proposed the orthogonal frequency division multiplexing (OFDM) system, in which a large number of orthogonal carriers are used and each carrier is modulated by phase shift keying (PSK) or quadrature amplitude modulation (QAM).
The OFDM system has the following characteristic. Specifically, because the whole of the transmission band is divided by a large number of subcarriers, the band per one subcarrier is narrow and thus the transmission speed is low. However, the total transmission speed is equivalent to that of related-art modulation systems.
Furthermore, the OFDM system has a characteristic that the large number of subcarriers are transmitted in parallel and thus the symbol rate is low. Therefore, the OFDM system also has a characteristic that the duration of the multipath relative to the duration of one symbol can be shortened and thus the susceptibility to the influence of the multipath can be lowered.
Moreover, data are allocated to the plural subcarriers. Therefore, the OFDM system has a characteristic that a transmitting circuit can be configured by using an inverse fast Fourier transform (IFFT) operation circuit that performs inverse Fourier transform in modulation and a receiving circuit can be configured by using a fast Fourier transform (FFT) operation circuit that performs Fourier transform in demodulation.
Because of the above-described characteristics, the OFDM system is frequently applied to digital terrestrial broadcasting, which is strongly susceptible to the influence of multipath interference. Examples of the standards of the digital terrestrial broadcasting employing the OFDM system include the integrated services digital broadcasting-terrestrial (ISDB-T) standard.
In the ISDB-T standard, in order to transmit additional information relating to transmission control of the modulated wave or seismic-motion warning information, it is prescribed to transmit an AC signal composed of 204-bit information as one unit by a predetermined subcarrier in OFDM symbols. The AC signal is an additional information signal relating to broadcasting.
The AC signal is subjected to differential BPSK modulation. The differential BPSK modulation is a modulation system in which the data string to be transmitted is subjected to differential encoding and the information (0, 1) resulting from the differential encoding is turned to complex signals (I-signal, Q-signal) having signal points of (+4/3, 0) and (−4/3, 0).
FIG. 1 is a diagram showing seismic-motion warning information of the AC (Auxiliary Channel) signal.
In FIG. 1, the numerals given below the respective pieces of information each represent the bit positions of the corresponding information on the basis of the beginning of the AC signal. The length of each piece of information in the lateral direction is not proportional to the number of bits.
As shown on the upper row of FIG. 1, the AC signal configured as one unit by 204-bit information is made up of a 1-bit reference signal of differential modulation, a 3-bit configuration identification, and additional information relating to transmission control of the modulated wave or seismic-motion warning information, composed of 200 bits, in that order from the beginning.
The reference signal is a signal serving as the reference amplitude and the reference phase of differential demodulation.
The configuration identification is a signal for identifying the configuration of the AC signal. 000, 010, 011, 100, 101, and 111 of the configuration identification indicate that additional information relating to transmission control of the modulated wave is transmitted. 001 and 110 indicate that seismic-motion warning information is transmitted. When the configuration identification is 001 or 110, the seismic-motion warning information is transmitted by the subsequent 200 bits.
The seismic-motion warning information is transmitted by the AC carrier of segment No. 0. The whole of the frequency band used in digital broadcasting compliant with the ISDB-T standard is divided into 13 segments from segment No. 0 to segment No. 12, and the carrier to transmit the AC signal (AC carrier) is prescribed for each segment.
The 200-bit seismic-motion warning information is made up of a 13-bit synchronization signal, a 2-bit start/end flag, a 2-bit update flag, a 3-bit signal identification, an 88-bit seismic-motion warning detailed information, a 10-bit CRC, and a 82-bit parity bit.
The synchronization signal is information indicating the beginning position of the seismic-motion warning information. Specifically, W0=“1010111101110” is inserted when the configuration identification is 001 and W1=“0101000010001,” which is the inverted word of W0, is inserted when the configuration identification is 110, alternately in units of frames.
The start/end flag is 00 when “seismic-motion warning detailed information is present,” and is 11 when “seismic-motion warning detailed information is absent.”
The update flag is incremented by one every time a change occurs in the contents of the series of seismic-motion warning detailed information transmitted when the start/end flag is 00, and notifies the receiver of that the signal identification and the seismic-motion information are updated.
The signal identification is a signal used for identifying the kind of seismic-motion warning detailed information, which follows the signal identification.
000 of the signal identification indicates that “corresponding region is present regarding seismic-motion warning detailed information,” and 001 indicates that “corresponding region is absent regarding seismic-motion warning detailed information.” That “corresponding region is present regarding seismic-motion warning detailed information” means that the subject region of the seismic-motion warning is present in the broadcasting area. That “corresponding region is absent regarding seismic-motion warning detailed information” means that the subject region of the seismic-motion warning is absent in the broadcasting area.
010 of the signal identification indicates that “corresponding region is present regarding test signal of seismic-motion warning detailed information,” and 011 indicates that “corresponding region is absent regarding test signal of seismic-motion warning detailed information.” 111 indicates that “seismic-motion warning detailed information is absent (broadcaster identification).” 100, 101, and 110 of the signal identification are undefined.
When the signal identification is any of 000, 001, 010, and 011, information on the current time when the seismic-motion warning information is sent out, information indicating the subject region of the seismic-motion warning, and information relating to the seismic source of the seismic-motion warning are transmitted as seismic-motion warning detailed information.
When the signal identification is 111, the broadcaster identification is transmitted as seismic-motion warning detailed information. When it is any of 100, 101, and 110, ALL1 is transmitted as seismic-motion warning detailed information.
The CRC is a CRC code generated by a generator polynominal about the bits from the 22-nd bit to the 112-th bit defined on the basis of the beginning of the AC signal.
The parity bit is an error correction code generated by a shortened code (187, 107) of a difference-set cyclic code (273, 191) about the bits from the 18-th bit to the 122-nd bit defined on the basis of the beginning of the AC signal.
The related art of the present invention is disclosed in e.g. STD-B31 <http://www.arib.or.jp/english/html/overview/doc/2-STD-B31v1—8.pdf>.